Electrical terminal blocks of the general kind to which this invention relates are quite commonly used in electric power plant and substation control circuits in considerable numbers. Their primary function is to permit interruption of the circuits, or a single circuit, for the temporary insertion of artificial loads or test equipment without disturbing the permanent wiring in the circuit. Among the performance requirements of terminal blocks are durability, since they are components of long-lived circuit construction; strength, especially during circuit opening and closing operations; safety during opening and closing; and positiveness of actuation.
Terminal blocks of the class to which the invention relates are shown in Blakeslee U.S. Pat. Nos. 1,836,951 (1931) and 1,891,212 (1932), and the structure of such terminal blocks has changed but little since then. Most more recent changes have been in the direction of reducing manufacturing costs, and not all of these have resulted in devices as satisfactory as Blakeslee's from an operational and safety standpoint.